Such an electronic device is known from U.S. Pat. No. 6,907,082, U.S. Pat. No. 6,972,584 or GB 2 229 897.
In the known devices, the modulation means comprises a variable resistor constituted by the collector-emitter path of a transistor. The transistor needs a minimum voltage drop across the collector-emitter path to properly work as a controllable current sink, and the current is controlled by adjusting this voltage drop which causes power dissipation.